I'm not sure how feasible throwing an error is - Type hints in Python can be arbitrary classes or instances thereof, in order to type hint for stuff like nested

I'm not sure how feasible throwing an error is - Type hints in Python can be arbitrary classes or instances thereof, in order to type hint for stuff like nested data structures (`Dict[str: int]`). You could disallow instances of specific built-in classes, but that seems... clunky, especially as some can be used in valid code (strings are used as forward references).